This invention relates generally to pumps and more specifically to piston type fluid intensifiers in which one fluid, in this case hydraulic oil, is used to increase the pressure of a second fluid, in this case air.
Fluid intensifiers may be of various configurations and used in many types of industrial devices. For example, the second, pumped fluids may be the same as, or even a portion of, the first, powering fluid as in the well-known "water rams" used in less developed areas to supply water under pressure from a stream.
Or the second fluid may be similar to the first but without intermixing as in oil driven fuel transfer pumps.
The fluids may even be of different types, i.e. one gas and the other liquid, as in air driven oil pumps or hydraulically driven air compressors.
It is this latter configuration which is of most interest in the present invention.
Compressed air is becoming more useful in many industrial applications, but one of the most demanding applications is in modern aircraft in which air is used for environmental support systems and for pneumatic control systems. Air is usually supplied to such systems, and for other uses, by bleeding a small amount of air from the compressor stages of the gas turbine propulsion engines or auxiliary power units. However, many modern gas turbines are designed so that very little excess air is available for such use even though sufficient power is available to drive a separate pump.
Prior art air pressure intensifiers have several problems which limit their life and/or reliability. Such intensifiers, or air compressors, are generally multi-stage, positive displacement types in which several pistons of graduated sizes (i.e. stages) are mechanically driven by a crankshaft or Scotch yoke mechanism. The first stage piston, and its check valves, tend to be quite large, resulting in high inertia forces when running at high speeds. These high inertia forces end to cause early failures, particularly in the check valves.
On the other hand, the last stage pistons are small but highly loaded from the pressure of the compressed air. This high face load, when combined with side forces from the crank or Scotch yoke, causes excessive bearing stresses on the side of the pistons resulting in rapid wear of the sealing parts. Typically, commercially available units have a mean time between failure of only about 500 to 1500 hours.
Furthermore, the geometry of a crankshaft driven unit results in a lot of wasted space which is only partly eliminated in the Scotch yoke design.
Thus, it should be apparent that there is need in the art for an improved air pressure intensifier.
A cursory search of the available prior art shows the following U.S. patents related to the general subject matter of the present invention: U.S. Pat. Nos. 2,293,097; 2,296,647; 2,508,298; 2,864,313; 3,059,433; 3,200,596; 3,809,502; 4,212,597; and 4,523,895.
In particular, the disclosures of U.S. Pat. Nos. 3,407,601 and 3,916,931 illustrate and describe some of the complexities and problems of such equipment.